An image forming apparatus which comprises an image read unit for reading an image and converting it into an image signal, a memory for holding the image signal, and an image output section for outputting the held image signal, and operates as a color copying machine has been proposed.
In addition, an image forming system has been proposed, which operates a color printer or operates both of a color copying machine and a color printer based on an instruction from the operator, in which the image forming apparatus and host computer are connected through a controller and which rasterizes, by the controller, color image information (PDL data) created by the host computer, holds the data in the internal memory of the controller, and then outputs the data from the image forming apparatus.
In such an image forming system, the controller has a large-capacity memory and compresses image information to store raster data corresponding an enormous number of pages in the memory.
In addition, while bitmapping PDL data, already bitmapped pages can be parallelly printed. The image forming apparatus is capable of double-side printing. The first surface pages are printed first and stored in an intermediate tray, and then, the second surface pages are printed from the intermediate tray. To print a document having pages in number larger than the stack count of the intermediate tray, paper sheets are repeatedly stacked/extracted in/from the intermediate tray in units of stack counts.
Communication control between the controller and the image forming apparatus in the prior art will be described.
The controller and image forming apparatus are connected by serial communication, and control commands are defined. As for the communication relationship, the controller serves as a master, and the image forming apparatus serves as a slave. Main control commands used for communication will be described below.
Status: A command for inquiring about the state of the image forming apparatus. The image forming apparatus returns “no paper”, “error”, “status (“operation in progress”, “door open”, and “prepare”)”, or “print report”.
Ready Page: The image forming apparatus is notified of information related to printable pages. The apparatus is notified of “the number of pages in the ready”, “paper feed/discharge positions”, and “color mode”.
Start: This command instructs the start of printing.
“Status” is transmitted every predetermined time. “Ready Page” is transmitted at least once before the start of printing. It may be transmitted during printing.
FIG. 6 shows the communication procedure between the controller and the image forming apparatus in executing double-side printing in the image forming system of the prior art.
In step S601, the controller sends “Status” to the image forming apparatus to inquire about its state.
In step S602, the image forming apparatus returns to the controller the paper state, the presence/absence of error, and the state of the image forming apparatus.
In step S603, pieces of information related to the page to be printed on the first surface are sent to the image forming apparatus. The controller sends to the image forming apparatus pieces of information including the number of pages, paper feed position, discharge position (intermediate tray), and color mode.
In step S604, the image forming apparatus stores the received information and notifies the controller of reception of data. If the image forming apparatus fails in storage, it transmits a resend request.
In step S605, pieces of information (the paper feed position is “intermediate tray”, the discharge position is “outside the machine”, and the like) related to the page to be printed on the second surface are sent to the image forming apparatus.
In step S606, the image forming apparatus notifies the controller that the pieces of received information are stored.
In step S607, the controller side instructs the start of printing. In step S608, the image forming apparatus side notifies the controller whether printing can be started. During printing, the controller periodically checks the state of the image forming apparatus by the “Status” command (S609) and knows whether the image forming apparatus has stopped upon receiving the number of printed pages in a print report “Report” (S610).
However, the conventional double-side printing has the following two problems. As the first problem, since the double-side printing uses the intermediate tray, paper feed to the intermediate tray and discharge from the machine are repeated. Hence, the productivity is low relative to through-path double-side printing using no intermediate tray.
As the second problem, since printing results of the first surface pages are temporarily stored in the intermediate tray, page processing is complicated, resulting in complexity in page control.